Paving grade bitumens

The bitumen and bituminous binders may be divided into three general groups (a) the paving grade bitumens, (b) the hard paving grade bitumens and (c) the oxidised bitumens. 

Paving bitumens are bitumens produced from the residue distillation of crude oil, whereas oxidised bitumens are produced from bitumen subjected to a blowing process during which oxidation of bitumen occurs. 

Paving grade bitumens in Europe are designated by the nominal penetration or viscosity ranges as appropriate. 

Paving grade bitumens according to CEN EN 12591 (2009) are divided into three groups (a) bitumen from 20 to 220 dmm in penetration, at 25°C (b) bitumen from 250 to 900 dmm in penetration, at 25°C and (c) soft bitumen, which are designated by kinematic viscosity, at 60°C. 

Paving grade bitumens are characterised by their consistency at intermediate (determined by penetration test), consistency at elevated service temperatures (determined by softening point or viscosity test) and durability (determined by resistance to hardening test). Their brittleness at low service temperature (determined by the Fraass breaking test) and temperature dependence of consistency (determined by the penetration index) may also need to be determined to meet regional requirements for specific conditions such as extreme cold or wide ambient temperature variations. Flash point is also determined as well as, optionally, the density. 

---

Table 3.2 Paving grade bitumen specifications for grades from 20 to 220 dmm penetration ...

Source Reproduced from CEN EN 12591, Bitumen and bituminous binders - Specifications for paving grade bitumens, Brussels CEN, 2009. With permission ( CEN). 

Hence, as in paving grade bitumen, a 10/20 dmm hard paving bitumen denotes that the penetration is expected to range between 10 and 20 dmm. 

Table 3.6 Specifications for hard paving grade bitumens... 

These additional properties are not part of the mandated essential characteristics but have been considered useful in specification of hard paving grade bitumens in some cases. Important - a restricted softening point range, of 5°C about a midpoint, shall be declared by the supplier the overall range shall be within the range in the table. 

Cut-back and fluxed bituminous binders are suitable for use in the construction and maintenance of roads, airfields and other paved areas. The bitumen used may be paving grade bitumen (in most cases) or by addition of polymer. 

The number after the letters corresponds to a viscosity class, the letters following notify the type of bitumen, B for paving grade bitumen and BP if with addition of polymer, whereas the last number corresponds to the class of setting ability. 

Hence, using Table 3.9, the characterisation Fm 4 B 6 indicates a medium-viscosity cutback or flux oil material based on paving grade bitumen that contains relatively volatile petroleum-based flux of which more than 55% distils at 225 C. 

The use of bitumen emulsions compared to cut-back bitumens and paving grade bitumens has the following advantages ... 

According to CEN EN 13808 (2013), a combination of letters and numbers is used to describe a bitumen emulsion. The cationic emulsions are designated by the letter C two numbers indicating the nominal binder content one or up to three letters such as B (for paving grade bitumen), P (for polymer-modified bitumen) and F (for bitumen with more than 3% [m/m] flux oil) and a number indicating the class of breaking behaviour. 

As an example, the designation of bitumen emulsion C 69 B 2 means that the emulsion is cationic, its nominal binder content is 69%, the bitumen contained is paving grade bitumen and its breaking value belongs to class 2 (rapid rate of breaking). 

Figure 3.11 Three-dimensional SBS thermoplastic elastomer network. (From Vonk W.C. and G. Van Gooswilligen, Improvement of paving grade bitumens with SBS polymers. Proceedings of the 4th Eurobitume, Vol. I, p. 299. Madrid, 1989.)...

The addition of elastomer to bitumen alters its characteristic properties, and the final product - the modified bitumen - becomes more elastic and less susceptible to temperature variations. Additionally, the modified bitumen with elastomers has better cohesion properties and higher resistance to ageing compared with the unmodified paving grade bitumen. 

The addition of elastomer also lowers the Fraass breaking point. As a result, the modified bitumen is expected to crack at lower subzero temperatures compared to unmodified paving grade bitumen. 

Vonk W.C. and G. Van Gooswilligen. 1989. Improvement of paving grade bitumens with SBS polymers. 

The softening point may be estimated from the penetration value. After extensive laboratory tests by the author, the following equation was derived, for paving grade bitumens with penetration ranging from 40 to 100 dmm, with a very good correlation coefficient (0.98) ... 

The penetration index (I ) indicates the temperature susceptibility of the paving grade bitumens, for grades 20130 to 160/220. The penetration index is calculated from the values of penetration, at 25°C, and the softening point determined. 

The limiting theoretical values of the penetration index are -10 for bitumens with very high susceptibility to temperature variations, up to +20 for bitumens almost independent of temperature variations. In practice, penetration index varies between -3 and +7 for paving grade bitumens and oxidised bitumens. The smaller the penetration index, the more sensitive the bitumen is to temperature variations. 

The Eraass breaking point provides a measure of brittleness of bitumen and bituminous binders at low (subzero) temperatures. The Eraass breaking point test was developed in 1937 (Eraass 1937) and began to be broadly used upon the advent of modified bitumens, since, by executing this test, the effect of the chemical additive on the behaviour of the modified bitumen could be determined. Nowadays, it has been adopted by many organisations and has been incorporated in European standards for specification requirements of paving grade bitumens (CEN EN 12591 2009) and of modified bitumens (CEN EN 14023 2010). 

The Heukelom chart also provides the facility to estimate the penetration index (PI) of paving grade bitumen. This is achieved by drawing a parallel line form the focal point, located on the chart, to the straight line obtained when plotting penetration and softening point. The penetration index is read from the intersection of the parallel line with the PI scale positioned on the chart. 

The flash point of the paving grade bitumens as determined by the Cleveland open cup method may vary from >165°C to >245°C for cut-backs of flashed bituminous binders, the flash point may be >160°C. 

The binder material for empirically or fundamentally specified AC mixtures can be conventional paving grade bitumen, modified bitumen or hard bitumen. The conventional... 

It is noted that the above applies only when the reclaimed asphalt has been produced with paving grade bitumen. 

BBTM consists of coarse aggregates of maximum nominal particle size (D) up to 10 mm (or 11.2 mm), fine aggregates 0/2 or 0/4 mm and binder. The binder can be paving grade bitumen. Natural asphalt and additives may also be added. 

The binder of BBTM may be paving grade bitumen, conforming to CEN EN 12591 (2009), or modified bitumen, conforming to CEN EN 14023 (2010). Natural asphalt conforming to CEN EN 13108-4 (2008), Annex B, may also be added. 

The selection of paving grade bitumen is based on regional climatic and traffic conditions. The author s opinion, after more than 10 years of experience with BBTM, is that a 35/50, 50/70 or 70/100 grade bitumen is sufficient in most cases. 

According to CEN EN 13108-2 (2008), when using more than 10% by mass of the total mixture of reclaimed asphalt from mixtures in which mainly paving grade bitumen has been used and when the binder added to the mixture is a paving grade bitumen and the grade of the bitumen is specified, the binder should conform to the requirements outlined in Section 5.4.1.1.1. 

BBTM temperatures at any place in the plant when produced with paving grade bitumen should be within the range of limits provided by CEN EN 13108-2 (2008). For paving grade bitumen 50/70 or 70/100, for example, the limit range is 140°C to 180°C. Measurements should be carried out in accordance to CEN EN 12697-13 (2001). 

The test temperature is that of mixing temperature plus 25°C, when paving grade bitumen is used, or plus 15°C on top of the reference mixing temperature defined by the supplier. 

---